I agree with all of the items on Twins89's list.
My dad died of cancer many many years ago and left us all with all the information we needed to help mom get through. Some of these included:
1) He made a list of life insurance policies, retirement, etc. complete with phone numbers and addresses. It was a god-send!
2) If you are well enough, try to label water lines -- bathroom sink, for example. Make sure your wife knows where the furnace shut-off is (if you have one). Dad created a notebook that indicated where the sewer cleanout was, which pipes supplied which water in the house, who to call if there was a problem, etc.
This is a wonderful gift you are giving your wife. It is very hard to accept one's own death and prepare others for a future without you. God bless you!
